The ice-nucleating ability of quartz immersed in water and its atmospheric importance compared to K-feldspar
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Published:2019-09-09
Issue:17
Volume:19
Page:11343-11361
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ISSN:1680-7324
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Container-title:Atmospheric Chemistry and Physics
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language:en
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Short-container-title:Atmos. Chem. Phys.
Author:
Harrison Alexander D.ORCID, Lever KatherineORCID, Sanchez-Marroquin Alberto, Holden Mark A., Whale Thomas F., Tarn Mark D.ORCID, McQuaid James B.ORCID, Murray Benjamin J.ORCID
Abstract
Abstract. Mineral dust particles are thought to be an important type of
ice-nucleating particle (INP) in the mixed-phase cloud regime around the
globe. While K-rich feldspar (K-feldspar) has been identified as being a particularly
important component of mineral dust for ice nucleation, it has been shown
that quartz is also relatively ice-nucleation active. Given quartz typically
makes up a substantial proportion of atmospheric desert dust, it could
potentially be important for cloud glaciation. Here, we survey the
ice-nucleating ability of 10 α-quartz samples (the most common
quartz polymorph) when immersed in microlitre supercooled water droplets.
Despite all samples being α-quartz, the temperature at which they
induce freezing varies by around 12 ∘C for a constant active site
density. We find that some quartz samples are very sensitive to ageing in
both aqueous suspension and air, resulting in a loss of ice-nucleating
activity, while other samples are insensitive to exposure to air and water
over many months. For example, the ice-nucleation temperatures for one
quartz sample shift down by ∼2 ∘C in 1 h and
12 ∘C after 16 months in water. The sensitivity to water and air
is perhaps surprising, as quartz is thought of as a chemically resistant
mineral, but this observation suggests that the active sites responsible for
nucleation are less stable than the bulk of the mineral. We find that the
quartz group of minerals is generally less active than K-feldspars by
roughly 7 ∘C, although the most active quartz samples are of a
similar activity to some K-feldspars with an active site density,
ns(T), of 1 cm−2 at −9 ∘C. We also find that the freshly
milled quartz samples are generally more active by roughly 5 ∘C
than the plagioclase feldspar group of minerals and the albite end member
has an intermediate activity. Using both the new and literature data, active
site density parameterizations have been proposed for freshly milled quartz,
K-feldspar, plagioclase and albite. Combining these parameterizations with
the typical atmospheric abundance of each mineral supports previous work
that suggests that K-feldspar is the most important ice-nucleating mineral
in airborne mineral dust.
Funder
Natural Environment Research Council Engineering and Physical Sciences Research Council
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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